Non-Maskable Interrupt. An IRQ 7 on the PDP-11 or 680[01234]0; the
NMI line on an 80[1234]86. In contrast with a
priority interrupt (which might be ignored, although that is unlikely),
an NMI is never ignored. Except, that is, on
clone boxes, where NMI is often ignored on the
motherboard because flaky hardware can generate many spurious ones.